proxy_upstream_next while no live upstreams

[Wu Bingzheng]

Because the last request before this 502-request was almost 20 minutes ago, so there was no error log in 20 minutes before this 502-request.

This is some strange, and only happens very rarely.

I know it's difficult to debug this if not reproduced. I just ask here to see if this is a known question.

Thanks for your answer.

Wu




At 2017-05-12 18:39:12, "Maxim Dounin" <mdounin at mdounin.ru> wrote:
>Hello!
>
>On Fri, May 12, 2017 at 01:24:14PM +0800, Wu Bingzheng wrote:
>
>> 
>> The last request before this 502 request is almost 20 minutes ago and its response code is 200.
>> 
>> The proxy_next_upstream conf:
>>     proxy_next_upstream error timeout invalid_header http_502 http_503 http_504;
>> 
>> Here is the access log. The upstream server 192.168.0.6 is DOWN. The line-10 is the 502 request:
>> 
>>   1 [03/May/2017:14:35:38 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.6:8181, 192.168.0.5:8181" 0.012 0.001, 0.011
>>   2 [03/May/2017:14:35:38 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.013 0.013
>>   3 [03/May/2017:14:54:30 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.206 0.206
>>   4 [03/May/2017:15:03:08 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.154 0.154
>>   5 [03/May/2017:15:40:51 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.6:8181, 192.168.0.5:8181" 0.012 0.000, 0.012
>>   6 [03/May/2017:15:40:51 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.014 0.014
>>   7 [03/May/2017:15:40:51 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.016 0.016
>>   8 [03/May/2017:15:40:51 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.017 0.017
>>   9 [03/May/2017:15:40:51 -0400] "POST /x/y HTTP/1.1" 200  "192.168.0.5:8181" 0.011 0.011
>>  10 [03/May/2017:15:59:06 -0400] "POST /x/y HTTP/1.1" 502  "192.168.0.6:8181, test_backend" 0.000 0.000, 0.000
>>  11 [03/May/2017:15:59:07 -0400] "POST /x/y HTTP/1.1" 200  "10.255.222.206:8181" 0.260 0.260
>
>Looking into response status code in access logs is not enough to 
>understand if a server is up or down.  For at least the following 
>reasons:
>
>- there might be over requests currently in flight which are not 
>  yet logged;
>
>- errors may occur while sending response body, and hence status 
>  code will not show if there was an error.
>
>It is usually a good idea to look into error logs instead.
>
>-- 
>Maxim Dounin
>http://nginx.org/
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